The general concepts of radar pulse integration, mean level detection, and batch/batch correlation between successive radar returns in the detection of targets are known to the adaptive video processing field and the radar video conversion arts. In Introduction to Radar Systems by Skolnik (1962), Chapter 9 is devoted to such topics as correlation, integration, and the digital detection of targets. In other references, the detection, by digital techniques, of targets in the presence of varying noise and electronic countermeasure levels and the problem of maintaining a low, well-regulated false alarm rate in differing radar environments have been considered. One such system is shown in U.S. Pat. No. 4,005,415. In that system, raw video data signals are processed digitally and threshold values generated based on computer-stored information. Beam-to-beam signal correlation between scans is also provided. In essence, the reference discloses a two-dimensional (2-D) and three-dimensional (3-D) radar system which provides target detection with a constant false alarm rate, despite the presence of clutter and electro-magnetic countermeasures (ECM). A varying signal threshold which depends on the average value of input video is used to maintain a fixed false alarm rate. Thresholding is provided by an adaptive threshold and detection element which has as inputs a plurality of triads, each triad having three input video lines. Although satisfactory in its data conversion, data processing, and weapons control functions, the digital system of U.S. Pat. No. 4,005,415 does not examine problems related to 2-D radar video processors having a plurality of parallel input channels. Further, although providing a variable threshold level in order to maintain a constant false alarm rate, azimuth integration, mean level detection, and batch/batch (as opposed to beam-to-beam) correlation were not considered. U.S. Pat. No. 3,281,834 also discloses use of digital methods in a radar application wherein a multi-level unit receives analog signals and converts them to digital form, the digital output being summed in an accumulator with readings previously stored in a memory. Another digital system is disclosed in U.S. Pat. No. 3,778,828 wherein range gating is employed for doppler processing. All of the above references, while employing digital means, do not address the problems associated with multiple video inputs which are integrated over azimuth and multiplexed into a single signal and do not provide for multi-level detection using azimuth integration, mean level detection, and batch/batch correlation. Further, none of the aforementioned references disclose the multiplexing of different forms of video inputs to produce a single signal carrying different types of data which can be processed serially, thereby optimizing data rate and data storage.
A prior art reference which does provide for a plurality of digitized input video radar signals is U.S. Pat. No. 3,964,064. In that reference, a multi-level video display wherein a plurality of thresholds are employed in the same detection apparatus is disclosed. However, the plurality of variable thresholds are not provided to maintain a constant false alarm rate as in the present invention.
The prior art has suggested methods of maintaining a constant false alarm rate in differing radar environments. Likewise the use of differing types of threshold detection has also been disclosed in some references.
However, the enhanced operation resulting from the simultaneous processing of different modes of video data, channeling the data through a plurality of different detection means, and providing a plurality of selectable thresholds which can be used in maintaining a constant false alarm rate has not been addressed by the prior art, particularly in a 2-D radar application.